1. Field of the Invention
The present invention relates to an ink jet recording head in which recording is performed by ejecting ink to form flying droplets, and a method of manufacturing the same.
2. Description of the Related Art
An ink jet recording head of the present invention can be applied to apparatuses for performing recording on a recording medium, such as printers, copiers, facsimiles having a communication system, word processors having a printer unit, and to industrial recording apparatuses made up of a combination of various processing apparatuses. Recording media on which the ink jet recording head of the invention can perform recording include papers, threads, fibers, textiles, leathers, metals, plastics, glasses, timbers, ceramics, and the like.
“Recording” in the invention means performance of recording on a recording medium of not only an image having a particular meaning such as a character or a figure but also an image having no particular meaning such as a pattern or the like.
3. Related Background Art
In recent ink jet recording heads, droplets of a discharged ink have become smaller and discharge ports have been distributed at a higher density in order to achieve recording with a higher image quality. There is a known technique in which elements such as an electrothermal transducer and a drive circuit therefor are provided in a board by means of a semiconductor manufacturing technique and an electrical control circuit (diode matrix circuit or shift register circuit) is built into a recording head. In an ink jet recording head manufactured by such a technique, ink is supplied to a plurality of discharge ports arranged in a line. The recording head has a through-cavity (hereinafter referred to as “supply port”) extending from the back surface of a substrate in a direction in which the electrothermal transducers are arranged, in communication with ink passages, thereby supplying ink from the common supply port to the individual discharge ports.
U.S. Pat. Nos. 6,540,335 and 6,137,510 disclose an ink jet recording head in which a supply port has a rib for suppressing the occurrence of residual bubbles and reinforcing a discharge-port-forming member to increase the strength thereof. Such an ink jet recording head having a rib is manufactured through the following steps:
(1) a step of forming an etch stop layer on a substrate surface having electrothermal transducers;
(2) a step of forming a back etching mask, functioning as a mask when forming a supply port, on the other surface not having the electrothermal transducers;
(3) a step of forming a pattern of ink passages and a rib on the substrate by using a layer of dissoluble resin;
(4) a step of forming a coating resin layer on the dissoluble resin layer;
(5) a step of forming discharge ports in the coating resin layer;
(6) a step of forming a supply port in the substrate;
(7) a step of removing the back etching mask;
(8) a step of removing the etch stop layer formed on the substrate; and
(9) a step of removing the dissoluble resin layer.
In the above ink jet recording head, the supply port is formed by chemically etching the substrate. More specifically, a supply port is formed by using a silicon substrate as the substrate and performing anisotropic etching with an etchant composed of a strong alkaline solution such as potassium hydroxide, sodium hydroxide, and tetramethylammonium hydroxide. In order to prevent the contact between the etchant and the coating resin layer, the etch stop layer is provided on the substrate by using a substance, such as silicon nitride, that is not easily dissolved by the etchant.
The etch stop layer is typically provided over a stepped portion in the surface of the silicon substrate. The etch stop layer is often slightly thinner at the stepped portion. Further, because of constraints and the like in a deposition apparatus, the thickness of the etch stop layer may vary in a single silicon substrate. With the variation in thickness of the etch stop layer or the like, when the silicon substrate is dissolved and the etch stop layer is exposed in the anisotropic etching step, a stress may be applied onto the etch stop layer itself resulting in the etch stop layer becoming irregularly cracked.
The substrate is typically covered with a native silicon oxide film. The native oxide film provided on the back surface of the substrate is to be removed by treatment with hydrofluoric acid after the anisotropic etching step. In that case, etching on regions where the etch stop layer is thinner, such as a stepped portion, may progress faster to expose the surface of the substrate.
After the above-described steps, a removal step by means of dry etching is performed in order to remove the back etching mask provided for forming the supply port. If the removal step is performed when there is a crack in the etch stop layer, an etching gas may enter into the substrate through the crack and erode the coating resin layer on the rib, leading to formation of irregular undulations.
If an ink jet recording head is manufactured in the above state, residual bubbles may stay at the eroded portion upon discharge thereby causing discharge failure due to incapability of supplying ink. Moreover, because of the irregular undulations formed on the rib, the discharge-port-forming member may be deformed so as to be incapable of maintaining sufficient strength to resist an applied external force, leading to an adverse effect on ink discharge. Such an external force is applied when a protective tape provided over the discharge-port-forming member is stripped in the process of distribution or when a suction cap or a wiping blade is brought into contact with the discharge-port-forming member during a recovery operation or the like.
In keeping pace with the increasing image quality of recorded images produced by ink jet recording heads in recent years, the number of discharge ports and the discharge port distribution density have increased, the length of lines of discharge ports has increased, the size of discharged ink droplets has decreased, and the number of colors thereof has increased. This has increased the number of wires to be connected to electrothermal transducers and the number of circuits required for more complicated drive control, resulting in an increase in substrate size. In order to address such a problem, a circuit can be configured, without increasing the size of a substrate, by increasing the number of wiring layers to be stacked on the substrate. In either case, however, the cost of manufacturing the recording head becomes high.